Dual-Neighborhood Wear Angle Automatic Detection Method

1. A dual-neighborhood wear angle automatic detection method for a four-ball friction tester, comprising: step 1: capturing a wear scar image of a test steel ball by an electron microscope and performing a gray processing on the captured wear scar image of the test steel ball to obtain a grayed wear scar image of the test steel ball; step 2: choosing a pixel arbitrarily in a defined center area of the grayed wear scar image of the test steel ball obtained in step 1, and constructing a proximal neighborhood above the pixel; step 3: calculating grayscale differences between the arbitrarily chosen pixel and pixels having first directions on a boundary of the proximal neighborhood; step 4: calculating deviation degrees of all pixels in the defined central area in the first directions based on the grayscale differences obtained in step 3; step 5: calculating a similar direction value based on the deviation degrees obtained in step 4; step 6: constructing a distal neighborhood of the arbitrarily chosen pixel chosen in step 2, and constructing focus pixels having second directions on a boundary of the distal neighborhood based on the similar direction value obtained in step 5; step 7: calculating grayscale differences between the arbitrarily chosen pixel and the focus pixels constructed in step 6; step 8: calculating deviation degrees of said all pixels of the defined center area in the second directions based on the grayscale differences obtained in step 7; step 9: calculating a direction value of a wear angle of the test steel ball based on the deviation degrees obtained in step 8; and step 10: calculating the wear angle of the test steel ball based on the direction value of the wear angle of the test steel ball obtained in step 9.

2. The dual-neighborhood wear angle automatic detection method for the four-ball friction tester according to claim 1, wherein the grayed wear scar image is a rectangular area having M pixel rows and N pixel columns; the defined center area refers to a rectangular area from a [0.25M]-th pixel row to a [0.75M]-th pixel row and from a [0.25M]-th pixel column to a [0.75M]-th pixel column of the grayed wear scar image; the constructed proximal neighborhood is a rectangular area having a width of w pixels in a column direction of the grayed wear scar image and a length of 2w pixels in a row direction of the grayed wear scar image; the arbitrarily chosen pixel is located in an i-th pixel row and a j-th pixel column of the grayed wear scar image and the pixels having the first directions on the boundary of the proximal neighborhood satisfy any of following formulas: {(k,l)|i−w≤k≤i and l=j+w}; {(k,l)|i−w≤k<i and i=j−w}; and {(k,l)|k=i−w and j−w≤l≤j+w}, where (k,l) represents a pixel having a first direction on the boundary of the proximal neighborhood and located in a k-th pixel row and an l-th pixel column of the grayed wear scar image.

3. The dual-neighborhood wear angle automatic detection method for the four-ball friction tester according to claim 2, wherein in step 3, said calculating the grayscale differences between the arbitrarily chosen pixel and the pixels having the first directions on the boundary of the proximal neighborhood comprises: on the constructed proximal neighborhood, sequentially and counterclockwise marking values of the first directions of the pixels on the boundary of the proximal neighborhood as 1, 2, . . . , 4w by taking a pixel (i,j+w) as a starting point; and calculating grayscale differences between the arbitrarily chosen pixel and the pixels having the first directions on the boundary of the proximal neighborhood in accordance with a following calculation formula:, d ⁡ ( i , j , α ) = { ❘ "\[LeftBracketingBar]" f ⁡ ( i , j ) - f W ( i , j , α ) ❘ "\[RightBracketingBar]" , [ 0.25 · M ] ≤ i ≤ [ 0.75 · M ] ⁢ and [ 0.25 · N ] ≤ j ≤ [ 0.75 · N ] 0 , else , where α represents a value of a first direction, f(i, j) represents a grayscale value of the arbitrarily chosen pixel in the defined central region, fw(i,j,α) represents a grayscale value of a pixel having the first direction on the boundary of the proximal neighborhood, d(i,j,α) represents a grayscale difference between the arbitrarily chosen pixel and the pixel having the first direction on the boundary of the proximal neighborhood, and [ ] represents a decimal rounding operation.

4. The dual-neighborhood wear angle automatic detection method for the four-ball friction tester according to claim 3, wherein in step 4, said calculating the deviation degrees of said all pixels in the defined center area in the first directions based on the grayscale differences obtained in step 3 comprises: setting the deviation degrees of said all pixels in the defined center area in the first directions as average values in the first directions of the grayscale differences obtained in step 3, and calculating the average values in accordance with a following formula:, h ( α ) = 1 N ′ ⁢ ∑ i = [ 0.25 M ] [ 0.75 M ] ∑ j = [ 0.25 N ] 0.75 N d ⁡ ( i , j , α ) , where α represents a value of a first direction, h(α) represents a deviation degree of pixels of the defined central region in the first direction, and N′ represents a total number of pixels in the defined center area.

5. The dual-neighborhood wear angle automatic detection method for the four-ball friction tester according to claim 4, wherein in step 5, the similar direction value is calculated based on the deviation degrees obtained in step 4 in accordance with a following formula:, α * = arg α ⁢ min ⁢ ( h ( α ) ) Where, α* represents the similar direction value.

6. The dual-neighborhood wear angle automatic detection method for the four-ball friction tester according to claim 5, wherein in step 6, the constructed distal neighborhood is a rectangular area having a width of W pixels in the column direction of the grayed wear scar image and a length of 2W pixels in the row direction of the grayed wear scar image, and the focus pixels having the second directions on the boundary of the distal neighborhood satisfy any of following formulas: {(K,L)|i−W≤K≤i and L=j+W}; {(K,L)|i−W≤K<i and L=j−W}; and {(K,L)|K=i−W and j−W≤L≤j+W}, where (K,L) represents a focus pixel having a second direction on the boundary of the distal neighborhood and located in a K-th pixel row and an L-th pixel column of the grayed wear scar image; wherein said constructing the focus pixels having the second directions on the boundary of the distal neighborhood based on the similar direction value obtained in step 5 comprises: determining pixels on a boundary box of the distal neighborhood that correspond to the similar direction value as the focus pixels having the second directions on the boundary of the distal neighborhood, wherein values of the second directions of the focus pixels satisfy:, [ α * - 1 w · W ] ≤ β ≤ [ α * + 1 w · W ] , where w<W≤40; and β represents a value of a second direction of a focus pixel on the boundary box of the distal neighborhood, and is an integer.

7. The dual-neighborhood wear angle automatic detection method for the four-ball friction tester according to claim 6, wherein in step 7, said calculating the grayscale differences between the arbitrarily chosen pixel and the focus pixels constructed in step 6 comprises: on the constructed distal neighborhood, sequentially and counterclockwise marking the values of the second directions of the focus pixels on the boundary of the distal neighborhood as 1, 2, . . . , 4W by taking a pixel (i, j+W) as a starting point; and calculating the grayscale differences between the arbitrarily chosen pixel and the focus pixels constructed in step 6 in accordance with a following formula:, e ⁡ ( i , j , β ) = { ❘ "\[LeftBracketingBar]" f ⁡ ( i , j ) - f W ( i , j , β ) ❘ "\[RightBracketingBar]" , if [ 0.25 · M ] ≤ i ≤ [ 0.75 · M ] ⁢ and [ 0.25 · N ] ≤ j ≤ [ 0.75 · N ] 0 , else where β represents a value of a second direction, f(i, j) represents a grayscale value of the arbitrarily chosen pixel in the defined central region, fW(i,j,β) represents a grayscale value of a focus pixel having the second direction on the boundary of the distal neighborhood, and e(i,j,β) represents a grayscale difference between the arbitrarily chosen pixel and the focus pixel having the second direction on the boundary of the distal neighborhood.

8. The dual-neighborhood wear angle automatic detection method for the four-ball friction tester according to claim 7, wherein in step 8, said calculating the deviation degrees of said all pixels of the defined center area in the second directions based on the grayscale differences obtained in step 7 is performed in accordance with a following formula: g(β)=Σi=[0.25M][0.75M]Σj=[0.25N]0.75Ne(i,j,β), where β represents a value of a second direction, and g(β) represents a deviation degree of pixels in the defined center area in the second direction.

9. The dual-neighborhood wear angle automatic detection method for the four-ball friction tester according to claim 8, wherein, in step 9, the direction value of the wear angle is calculated based on the deviation degrees obtained in step 8 in accordance with a following formula:, β * = arg β ⁢ min ⁢ ( g ( β ) , where β* represents the direction value of the wear angle.

10. The dual-neighborhood wear angle automatic detection method for the four-ball friction tester according to claim 9, wherein in step 10, said calculating the wear angle based on the direction value of the wear angle obtained in step 9 is performed in accordance with a following formula:, θ = { arctan ⁢ ( Y W ) , if ⁢ Z = 0 arctan ⁢ ( W W - Y ) , if ⁢ Z = 1 90 ⁢ ° if ⁢ Z = 2 ⁢ and ⁢ Y = 0 180 ⁢ ° - arctan ⁡ ( - W Y ) , else where θ represents the wear angle, Z represents a quotient of, β * - 1 W ,  which is an integer, and a value of Z is 0, 1, 2, or 3; and Y represents a remainder of, β * - 1 W ,  which is an integer, and a value of Y is 0, 1, 2, . . . , or W.

11. The dual-neighborhood wear angle automatic detection method for the four-ball friction tester according to claim 1, wherein the calculated wear angle of the test steel ball is used in at least one of: measurement of a diameter of a wear scar of the test steel ball, an adjustment of a shooting angle of the wear scar image of the test steel ball, and subsequent analysis and processing of wear intensity and density of the test steel ball.

12. The dual-neighborhood wear angle automatic detection method for the four-ball friction tester according to claim 11, wherein a wear resistance performance of a lubricant or grease is evaluated by an arithmetic average of diameters of wear scars obtained from measurements of three balls at a bottom of the four-ball friction tester.